Timber is a raw material used for manufacturing wooden articles. Timber is a product of a tree. Wood is made up of numerous tube like cells packed closely together. During the growth of the tree, these cells are positioned in a certain direction. The direction of these cells is referred to as the `grain'. The direction of the grain can be identified by the visible lines on the surface of the timber.
Any operation performed in the grain direction is called an operation `along the grain'.
Any operation performed at right angle to the grain direction is called `across the grain'.
Any irregularity occuring in the timber is a defect in the timber. These defects in the timber reduce its strength, durability and utility value.
Common defects in timber : A knot is caused due to the growth of branches on the tree. It appears on the surface of planks and on boards when the logs are sawn.
The following defects are caused due to uneven shrinkage, improper seasoning and defective storage.
• Twisting (Fig a)
• Cupping (Fig b)
• Cracking (Fig c)
Shakes
• Radial shake
• Star shake
• Cup shake
